The present disclosure relates to an image processing device, an image processing method, and a program, and more particularly, to an image processing device, an image processing method, and a program capable of performing a correction process on a false color or the like produced in an image photographed by a camera.
In an image photographed by a camera, a problem of aberration of a photographing lens occurs in some cases. Specifically, for example, chromatic aberration is one aberration caused due to the influence of lens aberration. Chromatic aberration occurs when a refractive index of light in a photographing lens of a camera differs depending on a wavelength, and causes a false color on an imaging surface.
As representative examples of the chromatic aberration, for example, axial chromatic aberration in which color blur occurs because a focal position on an optical axis differs depending on a wavelength and magnification chromatic aberration in which color deviation occurs because an image high-power differs due to a wavelength are known.
A false color of purple produced in the periphery of a high-contrast edge in which there is an overexposed pixel of which luminance reaches a saturated value is generally called purple fringe. This purple fringe is caused due to axial chromatic aberration or magnification chromatic aberration, and thus results in deterioration in image quality.
The color of the purple fringe is a color closer to purple in many cases. In practice, however, a color other than purple is produced in some cases due to lenses, photographing conditions, or the like. Here, a false color produced in the periphery of an overexposed high-contrast edge is referred to as purple fringe, irrespective of a color of the false color.
An occurrence cause and an occurrence region of the purple fringe will be described with reference to FIGS. 1(a) and 1(b).
FIG. 1(a) is a graph in which the horizontal axis represents a pixel position and the vertical axis represents a pixel value.
FIG. 1(b) is a schematic diagram illustrating a photographed image.
A Bayer array frequently used as a pixel array of an image sensor of a general camera includes pixels with three colors of red (R), green (G), and blue (B).
In FIG. 1(a), a region of pixel positions 0 to X1 is a so-called overexposed region in which the pixel value is the maximum. The pixel position X1 corresponds to an edge position at which the luminance value is sharply changed. A region of the pixel position X1 to a position subsequent to the pixel position X1 is a region in which the original pixel value is set to nearly 0.
Thus, a false color is produced since there is a difference between the pixel values of RGB due to chromatic aberration in the vicinity of the overexposed region in the periphery of the edge in which a pixel value is sharply changed from the overexposed region with the maximum pixel value.
In order to reduce the chromatic aberration, it is ideal to use a lens made of special material glass such as fluorite in which chromatic aberration hardly occurs. However, there is a disadvantage that a manufacturing cost is high.
Methods of reducing a false color produced due to such chromatic aberration by image processing are disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2009-124598 and Japanese Unexamined Patent Application Publication No. 2006-14261.
In processes disclosed in Japanese Unexamined Patent Application Publication No. 2009-124598 and Japanese Unexamined Patent Application Publication No. 2006-14261, however, a false color is detected and corrected using an RGB image after a de-mosaic process of setting all pixel values of RGB in respective pixels is performed through signal processing such as pixel value interpolation on a mosaic image in which one pixel value of RGB is set in each pixel output from an image sensor.
Accordingly, the processes disclosed in Japanese Unexamined Patent Application Publication No. 2009-124598 and Japanese Unexamined Patent Application Publication No. 2006-14261 may not be applied as processes on a mosaic image immediately output from the image sensor, that is, a mosaic image in which one pixel value of RGB is set in each pixel.
Further, Japanese Unexamined Patent Application Publication No. 2010-136225 discloses a process of removing a false color through image processing on a mosaic image before a de-mosaic process.
However, the disclosed process is merely a process performed on a Bayer-array image with a pixel array shown in FIG. 2(a) frequently used in cameras according to the related art.
On the other hand, in recent years, a problem has arisen in that the pixel density of image sensor has increased, the amount of incident light per pixel has decreased, and thus relative noise has increased. As a method of resolving this problem, an image sensor that has an RGBW array including all-wavelength transmission type white (W) pixels in addition to RGB colors has been suggested.
Specifically, an image sensor that has an RGBW array including white (W) pixels is shown in FIG. 2(b). A mosaic image which is an image photographed by an image sensor having the RGBW array and output from the image sensor is configured as a mosaic image in which only a pixel value of one color of RGBW is set in each pixel according to the pixel array shown in FIG. 2(b).
A technology for reducing purple fringe in a mosaic image photographed by an image sensor that has such an RGBW array has not been disclosed in the related art. Further, there is a problem that correction processes on an RGB array previously disclosed in the related art may not be directly applied.